Thermoplastic polymer fibre composition

ABSTRACT

Compositions suitable for producing mineral fibre reinforced thermoplastic composite materials by the wet-laid process comprise mineral fibres, matrix polymer and a coupling agent. The fibres are silanized with reactive silane groups capable of reacting with the coupling agent, for example a maleic anhydride grafted polyolefin, to improve adhesion between the fibres and matrix polymer in the final composite product. The composition excludes components which hinder the reaction between the silane groups and the coupling agent.

The present invention essentially concerns a composition suitable forthe preparation of a mineral fibre reinforced thermoplastic matrixpolymer composite material, a composite material and a process formaking same.

In the prior art, there is already known a surface treatment of glassfibres to improve adhesion with a polymeric matrix. Examples of thisprior art are JP-A-57-038548 and JP-A-60-046951, which latter disclosesa surface treatment of glass fibres by dipping them in an ammoniacalsolution of a copolymer of maleic anhydride and vinylacetate or anethylenic hydrocarbon of formula CnH_(2n) with n being from 2 to 5, anda silane coupling agent to provide silanized glass fibres.

In the prior art, there are also known mineral fibre reinforcedpolyolefin matrix composite materials, comprising mineral fibres, apolyolefin matrix and process aids. Most of them are prepared by a dryprocess based on melt extrusion. According to the melt extrusionprocess, all the components are mixed together and extruded when thepolymer component is molten to prepare the composition (see for instanceJP-A-60-001236). The compositions are said to have excellent mechanicalstrength.

In the composition, the mineral fibres used, usually glass fibres, canbe surface treated with a silane compound, such as an aminosilane.

Different processes are described in order to improve the adhesionbetween a polyolefinic matrix and a fibrous reinforcing material. Thus,GB-1,378,873 describes the use of a blend of an aromatic monocarboxylicacid or a carboxylic or polycarboxylic acid and a graft copolymerobtained by grafting an unsaturated dicarboxylic acid onto a propylenein a melt mixing and extrusion process of polypropylene and fiberglass.

U.S. Pat. No. 3,755,245 describes a composite obtained by injectionmoulding of a mixture of polypropylene, organic peroxide, a highmolecular weight halogenated organic compound and aminosilane heatedglass fibers.

Different processes are also described to prepare fiber glass withspecific coatings intended to have improved adhesion with thepolyolefinic matrix.

Thus, GB-A-1,174,943 describes inorganic fiber reinforced propylenepolymer molding compositions wherein the fibers are coated with thereaction product of aminosilane with anhydride modified polyolefin.

U.S. Pat. No. 4,426,469 describes a specific coating of fiber glass witha three component coating comprising a polyolefinic film forming agent,a silane and a bis-maleamic acid, and the use of these glass fibers toprepare blends with polyolefinic compounds which are treated byinjection molding.

U.S. Pat. No. 3,936,415 describes the preparation of glass fibers coatedwith a mixture of an organosilane coupling agent, an oxidized polyolefinand a carboxylated high molecular weight elastomer. These fibers arethen dried and used for the production of reinforced polyolefinicmatrix.

U.S. Pat. No. 3,661,628 describes another type of coated fiber glass andtheir use after being dried and mixed with olefinic polymers to formarticles through molding and extrusion.

Other similar melt extrusion prior art compositions are disclosed inJP-A-53-110645, JP-A-58-145750.

Finally, GB-A-1,262,470 (=FR-1,598,204) discloses a surface treatment ofinorganic surfaces to improve adhesion of organic coatings comprising acombination of an organosiloxane and of a copolymer of ethylenecontaining acid units. The disclosure of this document is very broad andthe uses disclosed concern coating of any silicous product, such asglass, in the form of panels, pearls, fibres, and notably to providesafety window glass (see page 4, lines 19 to 29). The siloxane alone ora mixture of the siloxane and the ethylenic copolymer containingcarboxylic acid groups are applied as a coating on the surface of thesubstrate (see page 4, lines 112 to 126). In the example given, thecoating binder comprises the ethylenic copolymer containing acidfunctions dispersed in an aqueous solution, in which has been introducedgamma-aminopropyl-(triethoxy)-silane; and a strand of fibre glass isimmersed in the aqueous solution (page 59, lines 95 to 121).

This patent only discloses and suggests a possible blend of glass fibreswith an olefin type resin by injection molding and simple extrusion(page 4, lines 53 to 60; page 6, lines 24 to 35).

A fully different way to prepare mineral fibres reinforced thermoplasticmatrix composite materials is by a wet-laid process, and there is nosuggestion in this GB document of the use of such silanized glass fibresin such a wet-laid process.

The wet-laid process for producing fibre reinforced thermoplasticcomposites has been known for some years, and in general employstechniques commonly used in papermaking in the preliminary stages. Thusa mixture of reinforcing fibres, powdered thermoplastics materials andoptionally dispersion aids, fillers, etc. is formed into a dilute slurrywith water. The slurry is then passed to a papermaking type machine anddelivered in a thin layer onto a moving mesh or "wire". The water isdrained off through the wire to leave a thin web of thermoplasticparticles in which are dispersed the reinforcing fibres. Because of theproduction method, the fibres, e.g. glass fibres, are arranged withtheir longitudinal axes in the plane of the web.

The web is dried, for example using hot air, at a temperature below thatat which the polymer fuses and the dried web is then converted into afused product by heating to a temperature at which the thermoplasticparticles melt and hence fuse into a continuous polymer matrix. coolingand shaping, e.g. by pressing into a mould whilst the polymer is stillmolten result in a fibre-reinforced thermoplastic polymer compositematerial of generally good physical/mechanical properties. When suchproduct is in the form of a flat two-dimensional sheet, it may bemoulded into three-dimensional articles by flow moulding (hot-pressing)technique.

Teachings relating to the wet-laid process may be found for example inU.S. Pat. No. 4,481,075, U.S. Pat. No. 4,645,565 and similar methodswhich also employ papermaking technology may be found for example inU.S. Pat. No. 4,734,321.

It has long been recognized in the art that teachings relating toproduction of melt extrusion compositions cannot be extrapolated toformulate compositions for a wet-laid process in view of the differenttechnical problems encountered in dispersing the composition componentsin an aqueous slurry. More particularly, the art of promoting fibre topolymer adhesion in a fused (continuous polymer phase) fibre reinforcedcomposite (final product) which is produced by a dry melt extrusionprocess cannot be applied to a wet-laid process.

Final products prepared via the wet-laid process have many advantagesover products obtained via the dry melt extrusion process. Thus, thereinforcing fibres in the mineral fibres reinforced polyolefin matrixcomposite often are subject to breakage when the composite is preparedby energy intensive methods such as extrusion and melt mixing. Althoughinterfacial adhesion of fibres to polymer can increase mechanicalproperties, such fibre breakage always lead to mechanical properties farless than expected, because fibre length is decreased during theproduction process. In contrast, the wet-laid process allows the fibreto maintain its integrity but interfacial adhesion of polymer to fibreis not achieved (resulting in mechanical properties also less thanexpected) because of the problems caused by the presence of water in theaqueous slurry used to lay down the composition.

So, there exists a performance need to achieve adhesion between fibresand the polymer matrix and to simultaneously retain fibre integrity. Theprior art solutions have to be improved as regards the adhesion/adhesionrate between the inorganic material (mineral fibre) and thethermoplastic (especially polyolefinic) matrix in the final compositematerial, as regards the length of inorganic material, with the purposeof improving the mechanical properties of the composite materials, ofsimplifying the method of preparation of improving the manufacturingrate.

A main purpose of the present invention is to solve the technicalproblem of improving sharply the adhesion between mineral fibresreinforcing a thermoplastic matrix in fused composite materials.

A further main object of the present invention is to solve the technicalproblem of improving adhesion between mineral fibres and athermoplastic, for example oleofinic, matrix in composite material,while allowing use of long mineral fibres, preferably having a lengthranging between 6 and 50 millimeters and most preferably between 10 and25 millimeters.

Another main object of the present invention is to solve the abovetechnical problem of improving the adhesion between mineral fibres and athermoplastic matrix in composite materials, whilst further allowingincorporation of large amounts of mineral fibres.

Yet another object of the present invention is to solve the technicalproblem of improving mechanical properties, notably impact strength,tensile and flexural strength, preferably improving the CHARPY impactstrength up to 50%, the tensile and flexural strength by a value rangingbetween 30 and 40%, in composite materials.

All these objects of the present invention may be solved simultaneouslyfor the first time by using a wet-laid process, which is very simple andlow cost, thereby being applicable on the industrial scale.

Therefore, according to a first aspect, the present invention provides acomposition suitable for the preparation, by a wet-laid process, of amineral fibre reinforced thermoplastic matrix polymer composite materialhaving improved adhesion between the mineral fibres and the matrixpolymer, comprising mineral fibres, thermoplastic polymer and optionallyprocess aids, characterized in that said mineral fibres are silanizedmineral fibres containing reactive silane groups, and in that saidcomposition further comprises an adhesion-promoting coupling agentcapable of reacting with the reactive silane groups, to improve adhesionbetween the mineral fibres and the polymer; said composition notcontaining components which would hinder significantly the reactionbetween the coupling agent and the reactive silane groups under theprocessing conditions of the wet-laid process.

The thermoplastic polymer of the defined composition may be anythermoplastic which finds industrial use, for example polyolefins,polyamides or polyesters. Particularly preferred are the polyolefinssuch as polypropylene, and hereinafter the invention is described interms of its applicability to polyolefins although it is to beunderstood that the particular embodiments described apply equally toother organic thermoplastic polymers.

According to a specific embodiment, the composition is characterized inthat it is contained in a slurry, said composition being dispersed inthe slurry, preferably at a content of from 0.1 to 5% by weight, e.g.about 0.5% by weight, said slurry being preferably an aqueous slurry.

Preferably, the coupling agent is a polyolefin modified with unsaturatedcarboxylic acid or anhydride groups, preferably having a content from0.2 to 5% by weight of grafted acid or anhydride groups, and mostpreferably from 0.5 to 2% of grafted acid or anhydride groups. Theseacid or anhydride groups, which are grafted, are preferably derived frommaleic, himic anhydride or acrylic acid.

According to a further embodiment, the composition is characterized inthat the coupling agent preferably has a molecular weight rangingbetween 5,000 and 250,000, depending on the nature of the thermoplasticpolymer, e.g. polyolefin, used to provide the matrix.

According to a special embodiment, the invention relates to acomposition wherein the content of the mineral fibres ranges between 15and 60 weight %; preferably between 20 and 50 weight % with regard tothe total weight of mineral fibres and thermoplastic polymer, e.g.polyolefin, the high mineral fibre content providing unexpected goodmechanical properties. The mineral fibres are preferably glass fibres,and according to another aspect of the invention, the mineral fibres arelong mineral fibres, preferably of a length ranging between 6 and 50 mm,most preferably between 10 and 25 mm. These are of course much longerthan the fibres which are typically present in melt extruded composites.The mineral fibres may have a diameter of for example from 8 to 20,preferably from 10 and 17 micrometers.

According to another invention embodiment, the composition ischaracterized in that the mineral fibres have been silanized with asilane surface coating selected from an aminosilane surface coating anda polysiloxane surface coating, which preferably represents less thanabout 1% by weight of the total weight of the mineral fibres.Preferably, the mineral fibres e.g. glass fibres, are also treated withan ionic species which functions to reduce agglomeration of the fibresin aqueous slurry. Such treatment with ionic species may take placebefore or after the fibres are silanized. The total of ionic andsilanized components on the mineral fibre is preferably no more than 1%by weight of the treated fibres. The ionic species which may be used totreat the fibres may be for example, an amphoteric or a cationicsurfactant such as dialkyl dimethyl ammonium salts or alkylbetaines,these being partially linked to the fibre in the treatment.

The proportion of coupling agent in the inventive composition preferablyranges between 0.5 and 25 weight %, preferably between 1 and 15 weight%, with regard to the total weight of the mineral fibres, thethermoplastic polymer, e.g. polyolefin and the coupling agent.

According to another embodiment of the invention, the composition ischaracterized in that it further comprises a dispersant for promotingdispersion of mineral fibres in water preferably in a content rangingbetween 0.05 and 15 weight %, more preferably 1 to 10 weight %, based onthe total weight of the mineral fibres. The dispersant will of course becompatible with the coupling agent, in the sense that it does not hindersignificantly the reaction between the coupling agent and the reactivesilane groups on the mineral fibres. Preferably, the dispersant is anionically charged polymer, not containing functional groups, such asamino or hydroxy groups, which would de-activate the coupling agent, ornot containing acid groups which would preferentially react withsilanized mineral fibres. Such a dispersant is, for example, analiphatic ester amide.

According to a further embodiment of the invention, the composition ischaracterized in that the thermoplastic polymer which, in the finalproduct, constitutes the matrix of the composite material, is in powderform having preferably a grain size of from 100 to 1000, more preferably300 to 800 micrometers.

In the composition of the invention, the thermoplastic polymer powdermay be optionally partially replaced with a polyolefin pulp, i.e. afibrillated polyolefin. This may be present, for example, in an amountof from 0 to 10 weight %, e.g. 1 to 20 weight %, more preferably 2 to 10weight % based on the total of fibres, thermoplastic polymer, couplingagent and pulp.

Further, the invention concerns a composition characterized in that itfurther comprises a flocculant, preferably in a content ranging between0.5 and 2 weight %, based on the total dry content of the composition;and/or an anti-oxidant, preferably in a content ranging between 1 and 2weight % based on the total dry content of the composition.

It is a feature of the inventive compositions, and of the processes inwhich they may be used in order to reach the target fused matrixreinforced composites, that they do not contain components, e.g. processaids, which would hinder the reaction between the reactive silane groupson the mineral fibres and the coupling agent. Hindrance of the reactionis here intended to include preferential reactions when thethermoplastic polymer is melted, and prior reactions which would "kill"the reactive species in the silanizing groups and the coupling agent.

The composition according to the invention may be in the form of amixture, e.g. in an aqueous slurry, or in the form of a dried web ofpolymer particles, coupling agent and silanized mineral fibres whichwill be permeable to air. The advantageous effect of the improvedadhesion between thermoplastic polymer component and fibre componentwill only be seen, though, when the web has been converted to a solidcomposite material wherein the thermoplastic is fused into a continuousmatrix in intimate contact with the fibres. Such conversion includes thestep of heating the composition to a temperature at least equal to themelting point of the thermoplastic matrix polymer.

Furthermore, the invention relates to a wet-laid process for preparing amineral fibre reinforced polyolefin matrix composite material, whichincludes forming a drained web from an aqueous slurry, characterized inthat the aqueous slurry is prepared with a composition as above defined,preferably said composition constituting from 0.1 to 5 weight % of theslurry. Preferably, the web is heated to a temperature sufficient tomelt the polyolefin and shaped to obtain a shaped composite material.

Further aims, objects, purposes and advantages of the invention willappear from the illustrative examples given herebelow. In the examples,all the percentages are given by weight unless otherwise stated.

COMPARATIVE EXAMPLE 1 Composite Material from a Polypropylene Matrix,Commercially Available Glass Fibres Having Ionic Surfactant Species(Diameter of 10 Microns, a Length of 13 mm), and a Cationic Dispersant,by a Wet-Laid Method

In 7 liters of water containing 3 g of a cationic dispersant based onfatty acid (Cartaspers® DS1 of Sandoz), 30 g of glass fibres which issized to have good dispersion in aqueous medium (reference HW618supplied by OWENS CORNING FIBERGLAS EUROPE) having an average length of13 mm and 10 microns diameter, are added with strong stirring. 6 g ofsynthetic pulp are then introduced with moderate stirring. Aftersuitable dispersion 64 g of polypropylene powder, of mean particle size700 microns are added. After dilution until the suspension containsabout 5 g of solids per liter, the mixture forming a "slurry" is thenadmitted on a wire screen, dewatered then dried according to theconventional papermaking technique. A sheet of 700 g/m² is thus obtainedwhich comprises sufficient cohesion to be handled, stored, transportedand in which the various components of the formulation have beenperfectly retained.

To make a final industrial product from this sheet, about 7 of suchsheets may for example be superposed and, after having effectedpreheating up to a temperature of the order of 180° C. to 210° C., theassembly may be moulded under pressures of 0,4-1 MPa (40-1CO kg/cm²) fora cycle less than 30 seconds.

COMPARATIVE EXAMPLE 2 Composite Material Made from the Same Compositionas Example 1, but with Silanized Glass Fibres

This example differs from the preceding one in that the glass fibres are10 microns diameter, 13 mm long and are sized with a silane to promoteadhesion as well as dispersion in aqueous medium (reference EC 690/2 byVetrotex).

COMPARATIVE EXAMPLE 3 Composite Material from the Same Composition as inExample 1, but with 6% of Coupling Agent

This example differs from example 1 in that 6 g of an unsaturatedcarboxylic acid modified polyolefin having 0.4% of grafted carboxylicacid chains from maleic acid origin (reference Exxelor® 2011 by ExxonChemical) is added into the aqueous solution and the amount ofpolypropylene is reduced to 58 g.

INVENTION EXAMPLE 4 Composition Material from the Same Composition as inExample 2, but with 6% of Coupling Agent of Example 3

This example differs from example 2 in that 6 g of Exxelor® 2011 isadded into the aqueous solution and the amount of polypropylene isreduced to 58 g.

It has to be noted that the dispersant used in examples 1, 2, 3 and 4are all "friendly" to adhesion.

INVENTION EXAMPLE 5 Same Composition as in Example 4, but withAdditional Flocculant

This example differs from example 4 in that 1 g of flocculant (referenceX8494 by Dow Chemical) is added into the aqueous solution.

INVENTION EXAMPLE 6 Composite Material from a Composition as in Example4, but with Use of Inert Carbon Black

This example differs from example 4 in that the PP granules is filledwith 1 g of carbon black. The black PP granules can be produced by firstmelt mixing white PP granules with carbon black masterbatch (referenceP30PPH by Cabot) followed by grinding.

COMPARATIVE EXAMPLE 7 Composite Material from a Composition as inExample 5, but with Use of a Dispersant Containing Hydroxy FunctionalGroups

This examples differs from example 5 in that 2 g of carbon blackdispersed in water at 0.35% slurry concentration (containing adispersant with hydroxy functional groups) (reference Tincolor BS byGMC) is added into the aqueous solution.

COMPARATIVE EXAMPLES 8, 9 Influence of Glass Fibres Content

These examples differ from example 1 in that 20 g and 40 g of glassfibres are used respectively and the amounts of polypropylene areadjusted accordingly to 68 g and 48 g.

INVENTION EXAMPLES 10, 11 and 12 Influence of Variation of Glass Fibresand Polypropylene Content

These examples differ from example 4 in that 20 g, 40 g and 50 g ofglass fibres are used respectively and the amounts of polypropylene areadjusted accordingly to 68 g, 48 g and 38 g.

INVENTION EXAMPLES 13, 14 and 15 Influence of the Length of Glass Fibres

These examples differ from example 10, 4 and 11 in that the glass fibresare 25 mm long, 10 microns in diameter, and are sized similarly to EC690/2 (reference R16EX20 by OWENS CORNING FIBERGLAS EUROPE).

INVENTION EXAMPLES 16, 17 and 18 Influence of Glass Fibres on Adhesion

These examples differ from examples 10, 4 and 11 in that the glassfibres are 16 microns diameter, 13 mm long, and are sized similarly toEC 690/2 (reference R16EX25 supplied by OWENS CORNING FIBERGLAS EUROPE).

All the composite materials obtained from the above examples 1 to 18 aresubmitted to measure of the mechanical properties, comprising measure ofthe Flexural Modulus according to DIN 53457; flexural strength accordingto DIN 53452, tensile strength according to DIN 53455 and unnotchedCHARPY impact strength according to DIN 53453.

All the results obtained are set forth in the table given herebelow.

    __________________________________________________________________________             EXAMPLES                                                                      1   2   3   4   5   6   7   8   9                                    __________________________________________________________________________    Fibres                                                                        HW618    30      30                  20  40                                   EC690/2      30      30  30  30  30                                           R16EX25                                                                       R16EX20                                                                       PP       64  64  58  58  58  58  58  68  48                                   Pulp      6   6   6   6   6   6   6   6   6                                   Coupling Agent                                                                          0   0   6   6   6   6   6   6   6                                   Dispersant.sup.+                                                                       10  10  10  10  10  10  10  10  10                                   Flocculant*           1           1                                           Carbon Black*             1                                                   Dis. Carb. Black*                 1                                           Flex Modulus                                                                           4500                                                                              4600                                                                              4700                                                                              4700                                                                              5003                                                                              5500                                                                              4200                                                                              3084                                                                              5600                                 Flex Strength                                                                          125 130 126 165 170 150 126 84  127                                  Tens Strength                                                                          83  90  88  108 98  98  82  51  88                                   CHARPY Impact                                                                          40  60  48  60  60  53  40  35  55                                   __________________________________________________________________________             EXAMPLES                                                                      10  11  12  13  14  15  16  17  18                                   __________________________________________________________________________    Fibres                                                                        HW618                                                                         EC690/2  20  40  50                                                           R16EX25              20  30  40                                               R16EX20                          20  30  40                                   PP       68  48  38  68  58  48  68  58  48                                   Pulp      6   6   6   6   6   6   6   6   6                                   Coupling Agent                                                                          6   6   6   6   6   6   6   6   6                                   Dispersant.sup.+                                                                       10  10  10  10  10  10  10  10  10                                   Flocculant*                                                                   Carbon Black*                                                                 Dis. Carb. Black*                                                             Flex Modulus                                                                           3568                                                                              6291                                                                              7504                                                                              3740                                                                              4546                                                                              5493                                                                              3957                                                                              5301                                                                              6494                                 Flex Strength                                                                          124 169 199 122 168 185 113 170 172                                  Tens Strength                                                                          77  122 158 73  108 122 56  97  105                                  CHARPY Impact                                                                          35  69  80  45  62  84  40  68  74                                   __________________________________________________________________________     .sup.+ % on FG content                                                        *% on total dry content                                                       Test methods used to measure flexural modulus, flexural strength, tensile     strength and unnotched Charpy strength are DIN 53457, DIN 35452, DIN 5345     and DIN 53453 respectively.                                              

The data set forth in the attached table are used to illustrate:

a) comparative example 1 versus comparative example 2 shows thatsilanization of Fiber Glass (FG) alone cannot increase properties. Theimpact strength was increased, but no simultaneous improvement instrength;

b) comparative example 3 versus comparative example 1 shows thatcoupling agent alone cannot increase properties;

c) invention example 4 versus comparative examples, 1, 2 and 3 showsthat the combined effect of silanization of FG and coupling agent is theonly way to achieve increase of both impact and strength properties. Thedispersant used in comparative examples 1, 2, 3 and 4 are all "friendly"to adhesion;

d) invention example 5 versus invention example 4 shows that theparticular flocculant used in invention example 5 is again "friendly" toadhesion;

e) example 6 versus example 4 shows that inert carbon black is also"friendly" to adhesion;

f) comparative example 7 versus examples 4, 5 and 6 shows that althoughthe flocculant and the carbon black are "friendly" to adhesion, thepresence of a very "unfriendly" dispersant in the carbon blackcompletely kills the adhesion. The dispersant used contains hydroxyfunctional groups;

g) comparative examples 8, 1, and 9 show that without adhesion, impactand strength properties enhancement due to increase of fibre glasscontent starts to level off at 40% FG level (compare examples 1 and 9);

h) invention examples 10, 4, 11, and 12 show that with adhesion, all themechanical properties continue to increase with increase of glass fibrecontent even up to 50% level;

i) invention examples 13, 14, and 15 show that 10 microns, 25 mm longfibre glass with sizing similar to the EC 690/2 when mixed with couplingagent (Exxelor®) can yield composites with very high properties viaadhesion;

j) invention examples 16, 17, and 18 show that thicker (16 micronsversus 10 microns) fibre glass with sizing similar to the EC 690/2 whenmixed with coupling agent (Exxelor®) can also yield composites with veryhigh properties via adhesion.

The conditions of drying of the web in the wet-laid process ensurechemical reaction between the coupling agent and the reactive silanegroups. An optimal complementary chemical reaction may occur when thethermoplastic polymer is molten.

We claim:
 1. A composition comprising:a) mineral fibres said fibres having a length in the range of from about 6 to about 50 millimeters, said mineral fibres being silanized with a coating having reactive silane groups, said mineral fibres also being treated with a surfactant; b) a coupling agent, said coupling agent including a polyolefin containing a grafted group, said grafted group being selected from the group consisting of an unsaturated carboxylic acid and an unsaturated anhydride; and c) a thermoplastic polymer.
 2. The composition of claim 1, characterized in that said composition is in the form of a slurry, said composition being dispersed in the slurry at a content in the range of from about 0.1 to about 5 percent by weight of the total weight of the slurry.
 3. The composition of claim 1, wherein said grafted groups are present in the range of from about 0.2 to about 5 percent by weight of said grafted groups based on the total weight of the coupling agent.
 4. A composition according to claim 1 characterized in that the content of the mineral fibres ranges between about 15 and about 60 weight percent based on the total weight of said mineral fibres and thermoplastic polymer.
 5. The composition of claim 1 characterized in that the mineral fibres have a diameter ranging between about 8 and about 20 micrometers.
 6. The composition of claim 1 characterized in that the mineral fibres have been silanized with a silane surface coating selected from a group consisting of an aminosilane and a polysiloxane, said silane surface coating being present at less than about 1 percent by weight of the total weight of the mineral fibres.
 7. The composition of claim 1 characterized in that the mineral fibres are glass fibres.
 8. The composition of claim 1 characterized in that the content of said coupling agent ranges between about 0.5 and about 25 weight percent based on the total weight of the mineral fibres, the thermoplastic polymer and the coupling agent.
 9. The composition of claim 1 characterized in that the surfactant is selected from the group consisting of an amphoteric and a cationic surfactant.
 10. The composition of claim 1 characterized in that said composition further comprises a dispersant present in a range between about 0.05 and about 15 weight percent based on the total weight of the mineral fibres; wherein said dispersant is substantially free from groups selected from the group consisting of amino, hydroxy and acid groups.
 11. The composition of claim 10, characterized in that the dispersant is an aliphatic ester amide.
 12. The composition of claim 1 characterized in that the thermoplastic polymer is a powder, said powder having a grain size in the range of from about 100 to about 1000 micrometers.
 13. The composition of claim 1 characterized in that said composition further comprises a polyolefin pulp present in the range of from about 1 to about 20 weight percent based on the total weight of said fibres, said thermoplastic polymer, said coupling agent and said pulp.
 14. The composition of claim 13, characterized in that said composition further comprises a flocculant, said flocculant being present in a range between about 0.5 and about 2 weight percent, based on the total dry content of the composition.
 15. The composition of claim 14, characterized in that said composition is in the form of an air-permeable web.
 16. The composition of claim 1 characterized in that the thermoplastic polymer comprises a polyolefin.
 17. The composition of claim 16, characterized in that the polyolefin comprises polypropylene.
 18. A mineral fibre reinforced thermoplastic polymer material in which the polymer comprises a continuous fused matrix, characterized in that said mineral fibre reinforced thermoplastic polymer has been prepared from the composition of claim 17 by a process which includes the step of heating the composition to a temperature of at least the melting temperature of the thermoplastic polymer.
 19. The composition of claim 4 characterized in that the mineral fibres have a diameter ranging between about 10 and about 17 micrometers.
 20. The composition of claim 7 characterized in that the content of the coupling agent ranges between about 1 and about 15 weight percent based on the total weight of the mineral fibres, the thermoplastic polymer, and the coupling agent.
 21. The composition of claim 11 wherein the thermoplastic polymer of the composite material is in a powder form, having a grain size in the range of from about 300 to about 800 micrometers.
 22. The composition of claim 12 characterized in that said composition further comprises a polyolefin pulp of a weight content in the range of from 2 to 10 percent based on the total weight of said fibres, said thermoplastic polymer, said coupling agent and said pulp.
 23. A composition comprising a slurry of:a) a thermoplastic polymer; b) silanized mineral fibres having a coating containing reactive silane groups; c) a polyolefin coupling agent, said coupling agent containing grafted groups selected from the group consisting of unsaturated carboxylic acid and unsaturated anhydride; and said silanized mineral fibres having been treated with a surfactant, said mineral fibres having a length in the range of from about 10 to about 25 millimeters.
 24. A composition comprising an aqueous slurry, said slurry containing in the range of from about 0.5 to about 5 percent by weight of the combination of:a) a polypropylene polymer; b) a coupling agent comprising polyolefin containing grafted unsaturated carboxylic acid groups, said polyolefin having a content in the range of from about 0.2 percent of about 5 percent by weight of said grafted acid groups; c) silanized mineral fibres characterized in that said silanized mineral fibres have been treated with a surfactant and said fibres have a length in the range of between about 10 and about 25 millimeters, said silanized mineral fibres further characterized in that the total of the silane or polysiloxane coating is about 1 percent by weight or less based on the total weight of the mineral fibres; said composition characterized in that the coupling agent ranges between about 1 and about 15 weight percent with regard to the total weight of the mineral fibres, the coupling agent, and the polypropylene polymer.
 25. In a process comprising:a) forming a slurry; b) forming a drained web; and c) drying the web;the improvement comprising forming the slurry according to claim
 2. 26. A process of using the composition of claim 1 comprising the steps of:a) forming a slurry according to claim 2; b) forming a web from the slurry; and c) drying the web at a temperature below that at which the polymer fuses.
 27. The process according to claim 26 wherein said coupling agent is polypropylene containing grafted functionality in the range of from about 0.2 to about 5 percent by weight of a group selected from groups consisting of an unsaturated carboxylic acid or and an unsaturated anhydride wherein said thermoplastic polymer is polypropylene.
 28. The process according to claim 26, wherein the slurry of step a) additionally comprises a dispersant wherein said dispersant is selected from the group consisting of an amphoteric surfactant and a cationic surfactant said dispersant being substantially free from groups selected from the group consisting of amino, hydroxy, and acid groups.
 29. The process according to claim 26 additionally comprising the step of d) heating the web of step c) to a temperature of at least the melting point of the thermoplastic matrix polymer.
 30. The process according to claim 29 additionally comprising the step of e) molding the heated web formed in step d) by subjecting it to pressures in the range of from about 0.4 to about 1 MPa (40 to 100 kg/cm) to obtain a shaped composite material.
 31. The process according to claim 30 wherein said shaped composite material comprises a two dimensional sheet.
 32. The composition of claim 1 characterized in that said surfactant is selected from the group consisting of dialkyldimethyl ammonium salts and alkylbetaines.
 33. In a process comprising the steps of:a) forming a slurry, said slurry containing;1) mineral fibres said fibres having a length in the range of from about 6 to about 50 millimeters, said mineral fibres being silanized with a coatings having reactive silane groups, said mineral fibres being treated with a surfactant; 2) a thermoplastic polymer; b) drying said slurry; the improvement comprising adding a coupling agent to said slurry, said coupling agent including a polyolefin containing a grafted group, said grafted group being selected from the group consisting of an unsaturated carboxylic acid and an unsaturated anhydride.
 34. A process for forming an air permeable web comprising the steps of:a) mixing in an aqueous slurry1) glass fibres said fibres having a length in the range of from about 6 to about 50 millimeters, said glass fibres being silanized with a coatings having reactive silane groups, said glass fibres also being treated with a surfactant; 2) a thermoplastic polymer; and 3) a coupling agent, said coupling agent including a polyolefin containing a grafted group, said grafted group being selected from the group consisting of an unsaturated carboxylic acid and an unsaturated anhydride; b) draining said slurry to form a web; and c) heating said web. 